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Help with Memory Interface and clock speed

I'm confused on how the GPU works with clock speed and memory interface.

Example:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487003&cm_re=780ti-_-14-487-003-_-Product

How does the 384-bit work with the 7000 Mhz?

Do you do 7000 * 1000 * 1000 (Convert to Hz) = 7,000,000,000 * 384 = 2,688,000,000,000 bits of data per second. Since the card has a memory capacity of 3 GB and 2.688 trillion bits = 2.32 GB per second, the card will take 1431 milliseconds to clear it's memory? I'm kind of lost.

Also why is there a different memory clock and core clock?


Edit: I read an article and I sort of understand now.
http://www.playtool.com/pages/vramwidth/width.html

How do you get 6.4 GB/s from "For example, a video card with 200 MHz DDR video RAM which is 128 bits wide has a bandwidth of 200 MHz times 2 times 128 bits which works out to 6.4 GB/s."
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  1. Best answer
    You calculated the 2.688 trillion bits/s correctly, but you seem to have gone a bit wonky when converting to GB/s.

    For the example you picked:

    (7000 x 384) / 8 = 336000 MB/s = 336 GB/s (the bandwidth, as listed in the specifications for that card)

    7000 is the speed of the memory in MHz
    384 is the bus width in bits
    8 is due to the fact there are 8 bits in a byte

    An alternative example, taken from a reference R9-290X (which has slower memory, but a wider bus):

    (5000 x 512) / 8 = 320000 MB/s = 320 GB/s


    As for the question of why there are different clocks for the memory and core, well they're two completely separate things; there's no need for them to be the same or anything.

    EDIT: just seen your edit. Give me just a sec, and I'll answer your new question for you.

    EDIT 2: For that example the 200 MHz speed has to multiplied by 2 because it's DDR RAM which stands for double data rate. So it becomes:

    (400 x 128) / 8 = 6400 MB/s = 6.4 GB/s
  2. Damn_Rookie said:
    You calculated the 2.688 trillion bits/s correctly, but you seem to have gone a bit wonky when converting to GB/s.

    For the example you picked:

    (7000 x 384) / 8 = 336000 MB/s = 336 GB/s (the bandwidth, as listed in the specifications for that card)

    7000 is the speed of the memory in MHz
    384 is the bus width in bits
    8 is due to the fact there are 8 bits in a byte

    An alternative example, taken from a reference R9-290X (which has slower memory, but a wider bus):

    (5000 x 512) / 8 = 320000 MB/s = 320 GB/s


    As for the question of why there are different clocks for the memory and core, well they're two completely separate things; there's no need for them to be the same or anything.

    EDIT: just seen your edit. Give me just a sec, and I'll answer your new question for you.

    EDIT 2: For that example the 200 MHz speed has to multiplied by 2 because it's DDR RAM which stands for double data rate. So it becomes:

    (400 x 128) / 8 = 6400 MB/s = 6.4 GB/s


    Wow thanks, that helped me out a lot!

    Were you suppose to add the GDDR5 multiplier to
    "7000 is the speed of the memory in MHz
    384 is the bus width in bits
    8 is due to the fact there are 8 bits in a byte"?

    (7000 * 5 * 384) / 8 = 1680000 MB/s = 1680 GB/S?

    Edit: Ah, 2.688 trillion was supposed to be bytes not bits. Forgot to divide by 8. :fou:

    Edit 2: Also, how does core clock correlate with memory clock? If you overclock the core clock, does it impact your memory clock? If so, how?

    Edit 3: Sorry about the amount of edits I'm making, but I'm just curious on what data is stored in the VRAM. I read that the data processed by the GPU is stored in the VRAM as a frame buffer, but what is this frame buffer? Pixel colors? Vectors? Textures?
  3. The GDDR5 multiplier as it were has already been applied; the actual memory speed is 1750 MHz. Unfortunately I can't for the life of me remember why it gets multiplied by 4 (as opposed to 2), but it does. You see the 1750 MHz reported in any monitoring program, like GPU-Z.

    EDIT: Whoops once again; just saw your edit :D

    EDIT 2: No, the two clocks are completely separate. You can overclock each one separately.
  4. Damn_Rookie said:
    The GDDR5 multiplier as it were has already been applied; the actual memory speed is 1750 MHz. Unfortunately I can't for the life of me remember why it gets multiplied by 4 (as opposed to 2), but it does. You see the 1750 MHz reported in any monitoring program, like GPU-Z.

    EDIT: Whoops once again; just saw your edit :D

    EDIT 2: No, the two clocks are completely separate. You can overclock each one separately.


    Ohh GDDR5 is quad data rate? Whoops.

    GDDR4 = 3
    GDDR3 = 2?

    DDR2 = 3?

    I'm confused :P

    Edit: Oh there is no GDDR4. So GDDR 3 is 3x data rate as well as DDR2? DDR3 is 4x?
  5. Sorry, I can't remember precisely why you have to multiply it by 4 sadly (I'm not sure I ever even new the real reason :p). I think it's down to something quite fundamental in how it works that leads to it transmitting 4 bits per clock cycle.

    Just to add, GDDR5 is just modified DDR3; GDDR5 has better bandwidth, but worse latency. DDR3 is simply double data rate; the reported speed is half of the actual speed (so 800 MHz for 1600 MHz RAM).
  6. Damn_Rookie said:
    Sorry, I can't remember precisely why you have to multiply it by 4 sadly (I'm not sure I ever even new the real reason :p). I think it's down to something quite fundamental in how it works that leads to it transmitting 4 bits per clock cycle.

    Just to add, GDDR5 is just modified DDR3; GDDR5 has better bandwidth, but worse latency. DDR3 is simply double data rate; the reported speed is half of the actual speed (so 800 MHz for 1600 MHz RAM).


    It happens 4 times per cycle right? Isn't that why you multiply it by 4?

    Why do you multiply the core clock by 2 to get memory and then 4 again to get the effective memory clock? That turns out to be a 6x multiplier.

    What do you mean by worse latency?
  7. By worse latency, I just mean worse than plain DDR3. It's a compromise to increase bandwidth, as that's more important in graphics usage (hence why DDR3 versions of graphics cards always perform worse than GDRR5 versions).

    I'm a little confused by your comment about core clock. Are you referring to the core clock on a graphics card?
  8. Damn_Rookie said:
    By worse latency, I just mean worse than plain DDR3. It's a compromise to increase bandwidth, as that's more important in graphics usage (hence why DDR3 versions of graphics cards always perform worse than GDRR5 versions).

    I'm a little confused by your comment about core clock. Are you referring to the core clock on a graphics card?


    Yes I am, the 780 Ti has a core clock of 876MHz, why do you multiply the core clock by 2 to find the memory clock? 876 * 2 = 1752; isn't the memory clock 1752?


    Or am I doing this wrong? I'm just trying to figure out how you get 7000 effective memory clock from the core clock.
  9. No, the core clock and memory clock are completely separate. The fact one is close to half the other is mere coincidence.
  10. Damn_Rookie said:
    No, the core clock and memory clock are completely separate. The fact one is close to half the other is mere coincidence.


    Ooh now I understand. Thanks!
  11. No worries, glad to help :) I wish I had more to impart, but I've already pushed the limits of my current knowledge with what I've said :D
  12. Damn_Rookie said:
    No worries, glad to help :) I wish I had more to impart, but I've already pushed the limits of my current knowledge with what I've said :D


    This really helped me, I can actually see why some graphics cards are better than others now.
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